The present application relates to molecular devices, imaging devices, photosensors, and electronic apparatuses. More specifically, the present application relates to a molecular device using an electron transfer protein, such as zinc-substituted cytochrome c, and an imaging device, a photosensor, and an electronic apparatus using such a molecular device.
Imaging devices with higher definition and higher sensitivity have been developed, and the pixel size has been reduced to reproduce a high-definition image. For CCD and CMOS sensors in the related art, however, a reduction in pixel size decreases the amount of charge that can be accumulated in each pixel, thus decreasing sensitivity. There is therefore a trade-off between reducing the pixel size and maintaining the sensitivity. It is suggested that the extension of the CCD and CMOS sensor technology will reach a ceiling sooner or later. The major reasons include that the CCD and CMOS sensors generate only one electron (one charge) from one photon and that it is difficult to reduce the pixel size to the order of several square micrometers or less.
On the other hand, proteins are promising functional devices as an alternative to semiconductor devices. While the miniaturization of semiconductor devices is thought to be limited to a size of several tens of nanometers, proteins provide sophisticated functions with much smaller sizes, namely, 1 to 10 nm. As a photoelectric transducer using a protein, the inventors have proposed a photoelectric transducer including a protein-immobilized electrode having zinc-substituted cytochrome c (horse-heart cytochrome c having zinc substituted for the central metal of the heme, namely, iron) immobilized on a gold electrode and have reported that the protein-immobilized electrode provides a photocurrent (see Japanese Unexamined Patent Application Publication No. 2007-220445 (Patent Document 1)). Because zinc-substituted cytochrome c has a size of about 2 nm, it can be used in a photoelectric transducer to form an extremely small pixel.
Also proposed is a color-image light-sensitive device including light-sensitive units having a photoelectric conversion function and formed of oriented films of photosensitive dye proteins, such as bacteriorhodopsin, carried on electrodes (see Japanese Unexamined Patent Application Publication Nos. 3-237769 (Patent Document 2) and 3-252530 (Patent Document 3). This light-sensitive device includes sets of light-sensitive units having photosensitive dye proteins sensitive to different wavelengths.
Furthermore, recently, the inventors have theoretically and experimentally clarified the mechanism of intramolecular electron transfer in photoexcited zinc-substituted cytochrome c and have proposed a molecular device based on that mechanism (see Tokita, Y.; Shimura, J.; Nakajima, H.; Goto, Y.; Watanabe, Y., J. Am. Chem. Soc., 2008, 130, 5302-5310 (Non-Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2009-21501 (Patent Document 4)).